linux-kernel - [PATCH 2/3]fs/inode: iunique() Optimize Performance

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Date:	Wed, 25 Nov 2009 22:12:19 +0800
From:	"Liuweni" <qingshenlwy@...il.com>
To:	"linux-kernel" <linux-kernel@...r.kernel.org>
Cc:	"viro" <viro@...iv.linux.org.uk>,
	"akpm" <akpm@...ux-foundation.org>, "jack" <jack@...e.cz>,
	"npiggin" <npiggin@...e.de>,
	"linux-fsdevel" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"strongzgy" <strongzgy@...il.com>, "xgr178" <xgr178@....com>,
	"Liu Hui" <onlyflyer@...il.com>
Subject: [PATCH 2/3]fs/inode: iunique() Optimize Performance

---
Change log:
Change the hash operation from division to shift. It will cost less time.
Also, I change the divisor from L1_CACHE_BYTES to L1_CACHE_SHIFT.
In the cache.h, the most L1_CACHE_BYTES defined as "(1 << L1_CACHE_SHIFT)".
---
Signed-off-by: Liuwenyi<qingshenlwy@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jan Kara <jack@...e.cz>
Cc: Nick Piggin <npiggin@...e.de>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

---
diff --git a/fs/inode.c b/fs/inode.c
index 4d8e3be..397d65f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -605,8 +605,8 @@ static unsigned long hash(struct super_block *sb, unsigned long hashval)
 {
 	unsigned long tmp;
 
-	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
-			L1_CACHE_BYTES;
+	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) >>
+			L1_CACHE_SHIFT;
 	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
 	return tmp & I_HASHMASK;
 }

 				
--------------
Best Regards,
Liuweni
2009-11-25

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